In a landmark study, Hirsch et al. used engineered autologous skin stem cells to replace more than 80% of the epidermis of a critically ill 7-year-old boy. The child suffered from junctional epidermolysis bullosa (JEB), a rare skin condition affecting fewer than 1 in 1 million people. Affected individuals have fragile skin that is prone to blisters and erosions, making them susceptible to life-threatening infections. The researchers obtained a small biopsy from a nonblistering skin section, which was used to grow keratinocyte cultures in the laboratory. Cells were engineered to express a skin protein called LAMB3 (which is defective in JEB), and grafts were transplanted onto the boy's denuded surfaces during multiple surgeries. At the 21-month follow-up stage, the boy's skin had healed normally, was blister-free, and was deemed fully functional with normal elasticity.